/*
 * To change this license header, choose License Headers in Project Properties.
 * To change this template file, choose Tools | Templates
 * and open the template in the editor.
 */

package encrypt;

/**
 *
 * @author XuanHung
 */
public class CTRMode implements BlockCipher
{
        byte[] X;
        byte[] Xenc;

        BlockCipher bc;
        int blockSize;
        boolean doEncrypt;

        int count = 0;

        @Override
        public void init(boolean forEncryption, byte[] key)
        {
        }

        public CTRMode(BlockCipher tc, byte[] iv, boolean doEnc) throws IllegalArgumentException
        {
                bc = tc;
                blockSize = bc.getBlockSize();
                doEncrypt = doEnc;

                if (blockSize != iv.length)
                        throw new IllegalArgumentException("IV must be " + blockSize + " bytes long! (currently " + iv.length + ")");

                X = new byte[blockSize];
                Xenc = new byte[blockSize];

                System.arraycopy(iv, 0, X, 0, blockSize);
        }

        @Override
        public final int getBlockSize()
        {
                return blockSize;
        }

        @Override
        public final void transformBlock(byte[] src, int srcoff, byte[] dst, int dstoff)
        {
                bc.transformBlock(X, 0, Xenc, 0);

                for (int i = 0; i < blockSize; i++)
                {
                        dst[dstoff + i] = (byte) (src[srcoff + i] ^ Xenc[i]);
                }

                for (int i = (blockSize - 1); i >= 0; i--)
                {
                        X[i]++;
                        if (X[i] != 0)
                                break;

                }
        }
}

